Context.Request.RawUrl different on 2 machines after rewrite

I have been bashing my head up against a wall trying to work out why on two vista machines running IIS 7.0.6000.16386 running the exact same code we get two different responses from Context.Request.RawUrl

The page is opened on each machine via a browser as

http://machine1.com/Regions/348/Adelaide.aspx
and
http://machine2.com/Regions/348/Adelaide.aspx